In the art of constructing a prestressed concrete tank in which, for example, wires are wrapped around the tank wall to put it into compression before any liquid is put into the tank, one problem has been the design of a satisfactory joint between the wall and the base of the tank. One way of making the joint was simply to fasten the wall rigidly to the base, for example, by cementing the wall into a groove in the base prior to any pretressing. However, the great forces needed for prestressing would create large bending moments in the wall before liquid was put into the tank, and the wall might crack. Another joint was made by placing the wall on a rubber pad on the base. The problem of buildup of excessive bending moments in the wall was eliminated because the wall could move inward against the elastic pad on prestressing and move back outward when the tank was filled. Such a joint is shown in Dobell U.S. Pat. No. 2,932,964. Unlike the case with the rigid joint, however, in the pad joint the base did not help to hold the wall against the pressure of the liquid, and the wall would move radially as the tank was emptied and refilled.